In a combustion chamber of a gas turbine system, an air-fuel mixture is burned whose exhaust gases cause the turbine of the gas turbine system to rotate, thereby converting the thermal energy of the combustion process into mechanical energy. For burning the air-fuel mixture, the combustion chamber is equipped with burners. The burners cause the fuel to be mixed with the air and the mixture to be combusted.
In order to ensure the reliability of supply and the flexibility of a gas turbine system, burners are nowadays used which can be operated with both gaseous fuels and liquid fuels. Such a burner is disclosed, for example, in DE 42 12 810 A1.
In view of the general efforts to reduce the pollutant emission of gas turbines, it is endeavored to avoid producing pollutants, particularly nitrogen oxides (NOX). The nitrogen oxides are essentially produced during the combustion process by molecular oxygen and molecular nitrogen being broken down and the atomic oxygen and atomic nitrogen then reacting with molecular nitrogen and molecular oxygen respectively to form nitrogen oxides.
In order to minimize the amount of nitrogen oxides formed particularly in the high load range, modern gas turbine systems are operated in what is known as premix mode. This means that the fuel is already mixed with air prior to ignition. This is in contrast to diffusion mode in which fresh air is fed to a burning air-fuel mixture and fuel is after-injected, the mixing of the fuel with the air not taking place until combustion. Diffusion mode is essentially employed during low-load operation and when starting up gas turbine systems. The different operating states of a gas turbine system are described e.g. in M. J. Moore “NOx emission control in gas turbines for combined cycle gas turbine plant” in Proc Instn Mech Engrs Vol 211, Part A, 43-52”. This also describes how inert substances such as water or steam can be added to the combustion mixture in gas turbine systems to reduce the pollutant emission in particular operating states. The water or steam then reduces the combustion temperature, which likewise brings about a reduction in the amount of nitrogen oxides.
The burner described in DE 42 12 810 can be operated in premix mode with both liquid fuels and gaseous fuels. For this purpose it comprises at least one liquid fuel line feeding into the air supply duct of the burner and at least one gaseous fuel line feeding into the air supply duct. The fuel lines are each assigned outlet ports through which the relevant fuel can be sprayed into the air stream leading to the burner, the outlet ports being adapted to suit the fuel supplied by means of the relevant fuel pipes in such a way that the fuel is well mixed with the combustion air flowing to the burner.    DE 44 15 315 A1 shows a burner wherein, prior to combustion of the air-gas mixture in a combustion chamber, liquid fuel is mixed with steam.    EP 1 143 199 A1 shows a combustor which is implemented as a lean premix combustor, wherein water and steam are injected into the combustor.    DE 101 60 907 A1 shows a burner wherein an operating mode for significantly reducing thermoacoustic vibrations is achieved by adding the fuel to the combustion stream and adapting the velocity of the fuel to the velocity of the flow of combustion air.